Question
A rectangular block of mass m and area of cross-section A floats in a liquid of density ρ. If it is given a small vertical displacement from equilibrium it undergoes oscillation with a time period T. Then:
Solution
B.
Force applied on the body will be equal to upthrust for vertical oscillations.
Let block is displaced through x m, then weight of displaced water or upthrust (upwards)
where A is area of cross-section of the block and 
is its density. This must be equal to force (=ma) applied, where m is mass of the block and 
is acceleration.
or 
This is the equation of simple harmonic motion.
Time period of oscillation
